A high performance Common Lisp compiler. In addition to standard ANSI Common Lisp, it provides an interactive environment including an a debugger, a statistical profiler, a code coverage tool, and many other extensions.

ECL (Embeddable Common-Lisp) is an interpreter of the Common-Lisp language as described in the X3J13 Ansi specification, featuring CLOS (Common-Lisp Object System), conditions, loops, etc, plus a translator to C, which can produce standalone executables.
ECL supports the operating systems Linux, FreeBSD, NetBSD, OpenBSD, Solaris and Windows, running on top of the Intel, Sparc, Alpha, PowerPC and ARM processors.

Nyquist is a language for sound synthesis and music composition. It is implemented in C and C++ and runs on Win32, OSX, and Linux. Nyquist combines a powerful functional programming style with efficient signal-processing primitives.

Lush is a Lisp dialect with extensions for object-oriented and array-oriented programming. Lush is intended for prototyping numerically intensive applications and is designed for easy integration of existing C/C++/Fortran codes.

A free and portable Common Lisp Webserver.
Portable AllegroServe is a variant of AllegroServe(tm) with an explicit emphasis on portability between Lispsystems and Operating Systems. You can find the original AllegroServe at https://github.com/franzinc/aserve
The best way to install Portable AllegroServe is through Quicklisp (http://quicklisp.org/). (The best way to install any Lisp library is through Quicklisp.)

NLISP is an extension to Common Lisp that provides an interactive numerical computation environment, similar to packages like Matlab and IDL. NLISP has array syntax, scientific plotting and a numerical library. It currently runs under CMUCL & SBCL Lisp.